As discussed in our earlier U.S. Pat. No. 5,793,323 issued to one inventor named in the present patent document the role of an electronic warfare radio receiver is to provide an operator with information indicating a search signal, a signal originating from for example a hostile radar apparatus, has discovered or at least been received at the operator""s location. This search signal may be as brief in its time duration as a single pulse of radio frequency A carrier signalxe2x80x94as indeed is in accordance with the practice used in modern stealth-considered radar equipment. Such a pulse of radio frequency carrier signal may in addition be of 100 nanoseconds or less duration in a present day radar system. From this short pulse width received signal it is nevertheless desirable to determine as much information as possible about the signal""s originating radar apparatus, especially such information as the carrier frequency and the spectral characteristics of the radar.
Although there exists a number of different types of wide band radio receivers capable of performing the functions of an electronic warfare receiver under idealized conditions, several of these receivers are large in physical size and expensive to build and maintain. In addition, when two signals arrive simultaneously at certain versions of these receivers i.e., two signals which are concurrent within a time interval such as one tenth of a microsecond, a signal processing difficulty is encountered. The processing of two signals separated by a time interval greater than this one tenth of microsecond is of course a much easier accomplishment and can be performed by a number of different broadband receiver types.
A receiver based on real time application of the discrete Fourier Transform mathematical function has been found to provide desirable performance characteristics in the electronic warfare environment. Fourier transform concepts have of course been known and used in other equipment for some time however difficulties in mechanizing certain parts of such apparatus in the real time and in the gigahertz operating frequency environment of current-day electronic warfare interest (and possibly within the size and weight limitations imposed by airborne or portable equipment requirements) have precluded use of such receivers for most non-laboratory purposes including military receivers.
Conventional wisdom in the electrical arts once suggested the implementation of a Fourier transform function for such a receiver using electronic components required the brute force adherence to the Fourier transformation mathematical definition and mechanization of mathematical multiplications, i.e., the consideration of real and imaginary components in the mathematical quantities or the signals appearing in the Fourier transform equation. In addition, the consideration of amplitude representations requiring several binary bits of data was once required by this conventional wisdom approach to the Fourier transform. These requirements were considered necessary in order to avoid the generation of spurious frequency components in the achieved Fourier transform function.
In recent years however we have demonstrated that an electronic warfare radio receiver of the monobit receiver type may use a unit value kernel function realization concept in implementing the discrete Fourier transform (DFT) thus eliminating the need for multiplication in this part of the receiver""s signal processing circuitry. Arrangements of this nature are disclosed in our prior U.S. Pat. Nos. 5,917,737 and 5,963,164, each issued in the name of one inventor of the present invention and one or more colleagues, patents originating in a U.S. Air Force laboratory. A most recent improvement in this single bit Kernel function arrangement is disclosed in the U.S. patent application of Ser. No. 09/944,616 a currently pending U.S. patent application of one present inventor and a colleague. Each of the herein identified patents/applications is hereby incorporated by reference herein.
The unit value kernel function concept has also been implemented in an application specific integrated circuit (ASIC) chip in this U.S. Air Force laboratory. The unit value Kernel function discrete Fourier transform concept and the arrangement of this integrated circuit chip have therefore been successfully demonstrated with real world electronic components. A single chip monobit electronic warfare radio receiver using this unit value Kernel function covers a 1.25 GHz instantaneous bandwidth and accomplishes a 256-point discrete Fourier transform in real time every 102.4 ns. This ASIC chip is being implemented in the form of a high speed field-programmable gate array in order to conveniently allow for improvements and includes arbitration logic determining the number of input signals and their frequencies. The encoding logic of this chip identifies the highest two amplitudes from a total of 128 (i.e., 256/2) frequency identification output signals.
An area for improvement in a monobit electronic warfare receiver according to the earlier of these patents concerns the achieved two-tone instantaneous dynamic range of the receiver possibly being undesirably low. The instantaneous dynamic range of a receiver relates to its ability to detect two simultaneous signals of different amplitude. If more than two signals of equal amplitude are received in a conventional electronic warfare receiver the receiver may respond by providing erroneous frequency information. In fact prior to our work with the monobit receiver no receiver could determine the presence of more than one signal and if the signals were false in nature. The monobit receiver is a resounding success in situations wherein the signal separation need is limited to 5 dB however if greater separations are needed then a more complex receiver is appropriate or an improvement to the monobit receiver as provided by the present invention is in order.
In fact with the approximation of the unit value Kernel function realization in a monobit receiver, when the four unit value algorithms of the U.S. Pat. Nos. 5,917,737 and 5,963,164 patents are used in a monobit receiver, the receiver is found to be capable of processing at least two input signals. The eight value Kernel function arrangement of the concurrently pending Ser. No. 09/944,616 patent application moreover provides improvement over the arrangements of these two patents with respect to dynamic range and other characteristics. The present invention provides yet additional improvement in this type of electronic warfare radio receiver.
The use of channelized radio receivers i.e., a radio receiver wherein an incoming radio frequency signal is divided into plural frequency-segregated segments is known in the electronic art. Such receivers perform the channelizing function for a variety of reasons including the accomplishment of differing signal processing steps in the different channels, the desired physical separation of hardware relating to different channels and the preclusion of cross channel interference effects. Some of these previous channelized receiver arrangements moreover involve signal processing employing the Fourier transformation mathematical operation. None of these prior receiver arrangements however result in an increase in the instantaneous dynamic range of the receiver, an increase in the number of simultaneous signals correctly identified nor employ a simplified Kernel function in their processing circuits all as disclosed in the present invention.
The present invention provides a monobit electronic warfare radio receiver in which a plurality of individual monobit radio receiver circuits are disposed in parallel in order to improve receiver performance.
It is therefore an object of the present invention to improve the instantaneous dynamic range of a real time-operating monobit electronic warfare radio receiver i.e., improve the instantaneous dynamic range of a monobit electronic warfare radio receiver capable of continuously processing input data without a data storage capability.
It is another object of the present invention to provide an electronic warfare radio receiver capable of processing several simultaneous signals.
It is another object of the present invention to provide an electronic warfare radio receiver in which input signals are processed in a plurality of segregated frequency channels or receiver circuits.
It is another object of the present invention to provide a monobit electronic warfare radio receiver in which the complexity of using plural radio receiver circuits is compensated-for by enabled simplifications within each radio receiver circuit.
It is another object of the present invention to provide a monobit electronic warfare radio receiver in which use of plural radio receiver circuits is compensated-for by the ability to use lowered signal sampling rates, a decreased number of sample points and a simplified analog-to-digital converter in each radio receiver circuit.
It is another object of the present Invention to provide a monobit electronic warfare radio receiver in which plural radio receiver circuits are arranged to avoid aliasing signal duplications between signals processed.
It is another object of the present invention to provide a monobit electronic warfare radio receiver in which use of plural radio receiver circuits is compensated-for by the ability to use lowered signal sampling rates, a decreased number of sample points and a software embodiment in each radio receiver circuit.
These and other objects of the invention will become apparent as the description of the representative embodiments proceeds.
These and other objects of the invention are achieved by a monobit electronic warfare radio receiver of improved instantaneous dynamic range and favorable simultaneous input signal characteristics, said radio receiver comprising the combination of:
electrical wave filter means for dividing an analog radio frequency input signal of said monobit electronic warfare radio receiver into an m-plurality of segregated frequency band-located analog component signals;
analog to digital converter circuit means for converting each of said m-plurality of segregated frequency band-located analog component signals to digital signals:
each said analog to digital converter circuit means having limited operating characteristics commensurate with respective of said segregated frequency-band frequency ranges:
individual radio receiver circuit channel signal processing means each comprising one of m radio receiver circuit channels of said monobit electronic warfare radio receiver;
said individual radio receiver circuit channel signal processing means each including one of m-number of n-point discrete Fourier transformation elements of limited transformation rate with respect to a rate needed for a complete (n) times (m)-point discrete Fourier transformation within a selected time interval;
said m-plurality of adjacent frequency band-located analog component signals incurring minimal dynamic range-limiting cross channel interference within said individual radio receiver circuit channels;
said monobit electronic warfare radio receiver including asimultaneously received radio frequency input signals processing capacity increased by a multiplying factor of said m-plurality size.